Gasoline fuel



' June 12,1962 R. v. KERLEY ETAL 3,038,792

- GASOLINE FUEL Filed March 20, 1959 PREFERRED I RANGE IIO EXHAUST VALVE LIFE, HOURS l l i I I I I I I I I I I I I I l I I I I I I I I l l l I I I I I I l l l I I l 0 I0 20* 4'0 so I00 BASE FUEL AROMATIC CONTENT, VOLUME PER CENT United States Patent 3,838,792 GASOLINE FUEL Robert V. Kerley, Birmingham, and Arthur E. Felt, Farmington, Mich assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware Fiied Mar. 20, 1959, Ser. No. 800,874 6 Claims. (Ci. 44-69) This invention relates to, and has as its chief object, the provision of self-scavenging leaded gasolines having greatly enhanced performance characteristics.

In the early 1920s, shortly after the momentous discovery of the great antiknock effectiveness of tetraethyllead, a disheartening discovery was made. This was that tetraethyllead alone could not be used in gasoline. It left solid deposits [in the engine] which resulted in serious exhaust valve burning and damage to the insulators and the electrodes of spark plugs. [T. A. Boyd, SAE Quart. Trans. 4, 188-9 (1950).] These troubles were corrected by adding to the gasoline an organic compound of bromine or of bromine and chlorine along with the tetraethyllead. Such halogen compounds prevented lead oxides from accumulating excessively on these critical engine surfaces by converting the lead to lead halides. The lead halides, being more volatile at engine combustion chamber temperatures than lead oxides, left the engine via the exhaust gas stream. This discovery of lead scavenging action thus paved the way for the commercial success of tetraethyllead.

Throughout the following decades the art, including continuous commercial practice, has considered the use with lead alkyl antiknocks of halogen scavengers to be essential. Tremendous efforts have gone into the development of more efiective halogen scavengers and more ideal concentrations and proportions thereof. Some of the great improvements resulting from these efforts are described in US. Patents 2,364,921; 2,398,281; 2,479,- 900; 2,479,901; 2,479,902; 2,479,903; 2,496,983; 2,661,- 379; 2,822,252; 2,849,302; 2,849,303; 2,849,304; 2,855,- 905; and 2,869,993.

Recently other types of lead scavengers have been proposed and evaluated. These include certain phosphorus compounds (U.S. 2,765,220; 2,828,195; 2,841,480; 2,843,465); sulfur compounds (US. 2,557,019); arsenic, antimony and bismuth compounds (US. 2,750,267; 2,819,156); tin compounds (US. 2,586,660); and so forth. One or two of these types of scavengers have enjoyed commercial usage as supplements to the commercially long-used halohydrocarbon scavengers. However, none of these newer scavengers has ever been commercially used in the absence of a halogen scavenger.

This invention provides a completely new approach to the scavenging problem and is a radical departure from preexisting concepts and practice. Excellent results have been achieved from its use.

This invention is a self-scavenging motor fuel composition for spark ignition internal combustion engines which essentially consists of a motor gasoline base stock and from about 1.20 to about 4.25 grams of lead per gal-Ion as an alkyllead antiknock agent, the base stock being characterized by having a content of aromatic gasoline hydrocarbons ranging from about 10 to about 60 volume percent based on the whole fuel. The balance of the base stock is composed of saturates, olefins, or both.

The present compositions are self-scavenging. By this is meant that they do not depend on and do not need any auxiliary additive to convert the combustion products of the lead into other chemical forms for more efiicient removal from the engine with the exhaust gases. For example, organic halide scavengers are not blended with the present compositions. Such scavengers are not needed. in fact, their presence would be detrimental because, as will be seen below, they can cause a depreciation in exhaust valve life. Thus, the present compositions themselves perform the scavenging functions and can thereby give better engine performance at much lower cost.

A critical feature of this invention is that the gasoline base stock must contain the above-specified substantial proportion of aromatic gasoline components. If this feature is observed, excellent engine performance (e.g., exhaust valve and spark plug life) is assured.

To illustrate this critical feature, a series of standard accelerated exhaust valve life tests were conducted. A CPR L-head engine was operated at wide open throttle at a constant speed of 900 r.p.m., an air/fuel ratio of 14.5 to 1 and a spark advance of 5 ATC. A modern multigrade motor oil was used as the crankcase lubricant. Exhaust valves where considered to be failed when a leakage rate of one cubic foot of air per minute escaping from the pressurized combustion chamber into the closed exhaust elbow was registered. This leakage rate has been found to correspond to a drop in compression pressure of 15 to 20 p.s.i. when measured at 260 rpm.

The base fuels used in these tests were either isooctane or various blends thereof with toluene. Isooctane is representative of parafiinic or saturate gasoline components whereas toluene represents aromatic gasoline components. In all cases, these base fuels contained 3.18 grams of lead per gallon as pure tetraethylleadi.e., no scavenging additive was used. Hence, these tests directly established the critical contribution of base fuel-type to the over-all excellent efiectiveness of the compositions of this invention.

For example, when the engine was run under the above conditions using the leaded isooctane, the average exhaust valve life is only 40 hours. Similarly, when the leaded fuel was too highly aromatic volume percent toluene, 25 volume percent isooctane) the average exhaust valve life is a mere 32 hours.

In sharp contrast, the fuels of this invention give exhaust valve lives that are more than 200 percent as great as the foregoing values. For example, the leaded fuel blends composed by volume of 10 percent toluene and percent isooctane and also 60 percent toluene and 40 percent isooctane have valve lives of at least 90 hours. Infact, when the percentage of aromatics in the total base fuel ranges from about 20 to about 55 percent by volumea preferred embodiment of this invention-the exhaust valve life is over hours, an average life of over hours being given when using equal volumes of toluene and isooctane as the base fuel.

Subjected to this same test procedure "was a fuel of this invention essentially consisting of a motor fuel gasoline base stock composed by volume of 42.1 percent aro maties, 7.4 percent olefins, and 50.5 percent saturates with which had been blended 3.18 grams per gallon of lead as pure tetraethyllead (no halide scavenger complement). The average exhaust valve life was over hours.

All of the foregoing test results are presented graphically in the FIGURE of the drawing. The abscissa represents the volume percentage of aromatics in the test fuels. Exhaust valve life, expressed in hours, is the ordinate. Hence, the higher the curve, the better was the exhaust valve durability.

Effective use of the above-described severe engine test involved correlating its results with dynamometer and road tests on passenger car engines. Extensive experience in evaluating fuel compositions-over 11 million miles of road operation and over 90,000 hours of engine dynamometer operation-has shown that an exhaust valve life in this severe test of about 90 hours is required to insure trouble-free valve performance when present-day engines are operated in normal service. Exhaust valve lives of less than about 80 hours portend poor performance on the road. Therefore, the fact that the compositions of this invention give average exhaust valve lives in this test of at least 90 hours establishes their excellence in normal service.

Other examples of the fuel compositions of this invention and their preparation are given below.

EXAMPLE I Blended to a concentration of 3.18 grams of lead per gallon was pure tetraethyllead with a motor gasoline base stock containing by volume 40.2 percent of aromatics, 5.6 percent of olefins and 54.2 percent of saturates. This base fuel had a specific gravity of 53.4 API (according to ASTM Test Procedure D-287), a vapor pressure (according to ASTM Test Procedure D- 323) of 8.0 p.s.i., and the following distillation characteristics (according to ASTM Test Procedure D86): An initial boiling point of 100 F., a percent point of 146 F., a mid-boiling point of 232 F., a 90 percent point of 331 F., and a final boiling point of 432 F.

EXAMPLE H In this instance the gasoline base stock was composed by volume of 35.2 percent of aromatics, 25.0 percent of olefins and 39.8 percent of saturates. Its gravity was 55.2 API and its vapor pressure was 8.1 p.s.i. It had an initial boiling point of 98 F., a 10 percent point of 150 F., a 50 percent point of 236 F., a 90 percent point of 317 F., and a final boiling point of 392 F. Pure tetraethyllead was blended with this base fuel to a concentration of 3.18 grams of lead per gallon.

EXAMPLE III A motor fuel containing 3.18 grams of lead per gallon as pure tetraethyllead was prepared from a gasoline base stock composed by volume of 42.5 percent aromatics, 10.8 percent olefins and 46.7 percent saturates. This fuel had a gravity of 53.5 API, a vapor pressure of 7.9 p.s.i., an initial boiling point of 102 F., a 10 percent point of 152 F., a mid-boiling point of 235 F., a 90 percent point of 320 F., and a final boiling point of 399 F.

EXAMPLE IV The base fuel used in this instance contained 39.6 volume percent aromatics, 4.7 volume percent olefins and 55.7 volume percent saturates. The fuel had a gravity of 54.8 API and a vapor pressure of 8.4 p.s.i. Its distillation characteristics were an initial boiling point of 100 F., a 10 percent point of 139 F., a mid-boiling point of 225 F., a 90 percent point of 318 F, and a final boiling point of 420 F. Blended with this fuel was pure tetraethyllead in amount such that there were 3.18 grams of lead per gallon.

EXAMPLE V Pure tetraethyllead was admixed with a base fuel composed by volume of 36.0 percent aromatics, 7.3 percent olefins and 56.7 percent saturates. Other characteristics of this base fuel were: Gravity, 55.2 API; vapor pressure, 8.5 p.s.i.; initial boiling point 95 F.; 10 percent point 137 F.; mid-boiling point 228 F.; 90 percent point 327 F.; and a final boiling point of 426 P. On completion of the blending operation, the resultant fuel contained 3.18 grams of lead per gallon. 1

EXAMPLE VI Pure tetramethyllead is blended with a gasoline composed by volume of 37.5 percent aromatics, 5.1 percent olefins and 57.4 percent saturates. Thebase fuel has a gravity of 553 API, a vapor pressure of 8.3 p.s.i., an initial boiling point of 97 F., a 50 percent point of 229 F., and a final boiling point of 432 F. The concentrations of tetramethyllead are adjusted so that one batch of fuel contains 1.2 grams of lead per gallon, another contains 2.4 grams of lead per gallon, a third contains 2.9 grams of lead per gallon, a fourth contains 3.5 grams of lead per gallon and a fifth contains 4.25 grams of lead per gallon.

EXAMPLE VII Three finished fuels are prepared from a base stock containing 23.7 volume percent aromatics, 15.7 volume percent olefins and 57.0 volume percent saturates. (Initial boiling point, F.; final boiling point, 392 F.) With one portion of this base fuel is blended pure tetrabutyllead to a concentration of 2.0 grams of lead per gallon. With another portion is blended methyltriethyllead to a concentration of 4.0 grams of lead per gallon. The third portion of this base stock is treated with an equimolar mixture of tetramethyllead, dimethyldiethyllead and tetraethyllead (no halogen scavenger is used) to a concentration of 3.75 grams of lead per gallon.

EXAMPLE VIII Pure tetraethyllead is blended with a gasoline composed by volume of 10 percent aromatics, 45 percent olefins and 45 percent saturates. The lead concentration is 3.0 grams per gallon.

EXAMPLE IX Admixed with a gasoline base stock composed by volume of 60 percent aromatics, 20 percent olefins, and 20 percent saturates is pure diethyldimethyllead to a concentration of 2.6 grams of lead per gallon.

To further demonstrate the excellence of the fuels of this invention, an extensive series of standard engine durability tests was conducted. These tests involved use of multicy-linder engines mounted on engine dynamometers. These engines were operated on standard cycling schedules of speed and load to simulate vehicle operation in suburban-type s-top-and-go driving, followed by a period of turnpike driving. Two makes and three models of engines were used. One was a 1955 V-8 engine having a compression ratio of 8.5: 1, a displacement of 324 cubic inches, a bore of 3.875 inches and a stroke of 3.4375 inches. It was equipped with a standard four-barrel carburetor.

The test cycle for this engine involved a continuous cycle of 16 test hours of suburban-type operation followed by 6 test hours of turnpike operation. In the suburban phase of operation, the engine was alternately operated between an engine speed of 1800 revolutions per minute (r.p.m.) (for seconds) and 550 r.p.m. (for 40 seconds). At 1800 r.p.m. the operation was equivalent to a vehicle speed of 45 miles per hour (m.p.h.) at a basic road load of 17.0 inches of mercury manifold vacuum. Under these conditions the fuel/air ratio ranged from 0.067 to 0.71, the ignition timing being 37.5 BTC (Before Top Dead Center). The operation at 550 con sisted of idle operation. The acceleration from idle to 45 mph. involved a seven-second period of acceleration.

The turnpike phase of operation for this engine comprised an engine speed of 2600 r.p.m. (equivalent to 65 mph), a fuel/air ratio ranging from 0.062 to 0.066 and an ignition timing of 43.5 BTC.

Another engine used in these tests was a 1957 V-8 engine having a compression ratio of 8.5 :1, a displacement of 283 cubic inches, a bore of 3.875 inches and a stroke of 3.00 inches. This engine was equipped with a standard two-barrel carburetor. This engine was operated on a similar cycling schedule alternating between suburban-type operation and turnpike operation.

The third engine was a 1959 six-cylinder in-line engine having a compression ratio of 8.25:1 and equipped with a standard single-barrel carburetor. It had a displacement of 235 cubic inches, a bore of 3.56 inches and a stroke of 3.94 inches. The cycling schedule was similar to those described above.

The fuel compositions of Examples I through V were subjected to cycling tests described above for periods ranging from 502 to 532 hours in length. There was not one single instance where exhaust valve failure or spark plug failure was encountered. In each instance, the test was arbitrarily terminated. Thus, in tests involving a total of 3100 hours of operation under this suburban-turnpike type of operation, in which three different engine types were used, the fuel compositions of this invention exhibited perfect performance.

A comparative series of tests was conducted, the chief variable being that the base fuels contained a conventional scavenger complement in addition to the tetraethyllead. Thus, these fuels were comparable to those described in Examples I through V with the exception that they contained, in addition to 3.18 grams of lead per gallon as tetraethyllead, 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride. Hence, these tests served as a direct index of the performance characteristics of present-day commercial motor gasolines. The tests involved use of two of the above engine typesthe 1955 V-8 engine and the 1957 V-8 engine-but otherwise the test conditions were identical. It was found that in two instances the exhaust valve life exceeded 500 hours of operation. In the remainder of the tests, exhaust valve failures were encountered, the exhaust valve life (as measured by hours to the first exhaust valve failure) averaged 323 hours. Generally speaking, spark plug performance was satisfactory, although in two tests spark plug failures occurred. The data are presented in the following table.

this severe test was carried out on a fuel of the invention-3.18 grams of lead per gallon as pure tetraethyllead in a base fuel composed by volume of 36.0 percent of aromatics, 7.3 percent of olefins and 56.7 percent of saturates, it was found that no exhaust valve difficulties were encountered after 1211 hours of operation. In fact, when this test was terminated, there was no indication whatsoever of any impending exhaust valve failure.

The fuels of this invention possess still further technical advantages. For example, it has been found that the fuels of this invention produce significantly lower rates of piston ring wear than comparable fuels containing organic halide scavengers. In addition, engine tests have shown that the fuels of this invention provide marked reductions in inlet valve underhead deposits as compared with corresponding fuels containing conventional organic halide scavengers.

As stated above, a critical feature of this invention is that the base stock must contain from about 10 to about 60 volume percent of aromatic gasoline hydrocarbons. An excellent source of these aromatic hydrocarbons is catalytic reforming. The remainder of the base fuel is composed of saturates, olefins, or both. The olefins are generally formed by using such procedures as thermal cracking, catalytic cracking and polymerization. Dehydrogenation of paraffins to olefins can supplement the gaseous olefins occurring in the refinery to produce feed material for either polymerizaion or alkylation processes. The saturated gasoline components comprise paraifins and naphthenes. These saturates are obtained from (1) virgin gasoline by distillation (straight run gasoline), (2) alkylation processes (alkylates) and (3) isomerization Table.Efiect of Motor Fuel Composition on Engine Performance Fuels of This Invention Fuels Not: of the Invention Engine Fuel Oompo- Test Exhaust Spark Test Exhaust Spark sition Used Length, Valve Plug Length, Valve Plug Hrs. Life, Hrs. Life, Hrs. Hrs. Life, Hrs. Life, Hrs.

370 300 370 250 145 25 {Example I. 520 520 520 285 253 243 Example I..- 503 503 503 352 313 3 515 515 276 457 415 457 Example II 523 523 523 375 338 230 1957 V-s Example III 532 532 532 504 504 431 Example IV 502 502 502 549 496 549 1959 6 Example V 520 520 520 Average 517 517 364 351 a Spark plugs replaced during test Without being failed.

The fuels of this invention have been shown to give excellent results when subjected to severe road operation. For example, a fuel of this invention was used to operate a 1958 car having a V8 engine, a four-barrel carburetor and a compression ratio of 10:1. This car was operated on a twenty-four hour schedule over essentially rolling terrain accumulating about 5200 miles per week at an average speed of 56 m.p.h. The fuel was composed of a gasoline base stock containing by volume 21.0 percent of aromatics, 18.8 percent of olefins and 60.2 percent of saturates with which had been blended pure tetraethyllead to a concentration of 3.18 grams of lead per gallon. It was found that no exhaust valve difficulties had been encountered after operating this car under these severe conditions for over 87,000 miles.

Even under exceedingly heavy-duty engine operating conditions, the fuels of this invention have been shown to give exceptionally good exhaust valve performance. For example, a 283 cubic inch V-8 truck engine mounted on an engine dynamometer stand was operated on a very heavy-duty cycling schedule to measure exhaust valve life under drastic operating conditions. This cycling schedule alternated between 182 seconds at 3200 rpm. full throttle and 800 rpm. idle for 46 seconds. When procedures (conversion of normal paraffins to branched chain paraflins of greater octane quality). Saturated gasoline components also occur in so-called natural gasoline. In addition to the foregoing, thermally cracked stocks, catalytically cracked stocks and catalytic reformates contain saturated components.

The above classification of gasoline components into aromatics, olefins and saturates is well recognized in the art. Procedures for analyzing gasolines and gasoline components for hydrocarbon composition have long been known and used. Commonly used today is the FLA analytical method involving fluorescent indicator absorption techniques. These are based on selective absorption of gasoline components on an activated silica gel column, the components being concentrated by hydrocarbon type in different parts of the column. Special fluorescent dyes are added to the test sample and are also selectively separated with the sample fractions to make the boundaries of the aromatics, olefins and saturates clearly visible under ultraviolet light. Further details concerning this method can be found in ASTM Standards on Petroleum Products and Lubricants, November 1957 Edition, under ASTM Test Designation D 1319-56T.

The motor gasoline base stocks used in formulating the improved fuels of this invention generally have initial boiling points ranging from about 80 to about 105 F. and final boiling points ranging from about 380 to about 430 F. as measured by the standard ASTM distillation procedure (ASTM D86). Intermediate gasoline fractions boil away at temperatures within these extremes.

Methods for the preparation of alkyllead antiknock agents used in the practice of this invention are well known and reported in the literature. For example, recourse may be had to the alkyllead manufacturing processes described in U.S. Patents 2,414,058; 2,535,190-193; 2,535,235-237; 2,558,207; 2,562,856; 2,574,759; 2,575,- 323; 2,591,509; 2,594,183; 2,594,225; 2,621,199; 2,621,- 200; 2,635,105; 2,635,107; 2,660,591-596; 2,688,628; 2,727,053; 2,859,225-226; 2,859,228232; etc. Generally speaking, the tetraalkyllead antiknock agents used in the fuels of this invention can contain from 4 to about 20 carbon atoms in the molecule, although on a cost-effectiveness basis, tetraethyllead is preferred.

As pointed out above, conventional scavenger additives are not and should not be used in the compositions of this invention. Among the reasons for this is that the co-presence of conventional scavenger additives can be and frequently is harmful. For example, the deliberate addition of conventional organic halide scavengers to the fuels of this invention adversely affects the exhaust valve performance characteristics of the fuels. Consequently, organic halide scavengers are not deliberately added to the compositions of this invention; in other words, the fuels of this invention are essentially free of halogen. However, it should be understood that trace quantities of organic halide scavengers can be tolerated in the fuels of this invention. To illustrate, engine tests have shown that trace quantities of ethylene dibromide and ethylene dichloride (present in certain fuels of this invention by virtue of contamination through prior use of blending and storage equipment) produced no detectable adverse effect upon the performance characteristics of the fuels.

Another reason for not adding organic halide scavengers to the fuels of this invention is that decided cost advantages are maintained.

Certain other additives can be used in the compositions of this invention. Hence, as used in this description and in the appended claims, the phrase essentially consisting of is intended to mean that the compositions of this invention are devoid of conventional scavenger additives (other than trace quantities incurred through contamination) and also that any other ingredient of these compositions is selected with due regard to the principles given below.

Antioxidants can be effectively used in the compositions of this invention. Particularly useful materials for this purpose are N,N-di-sec-butyl-p-phenylene diamine, p-N- butylaminophenol, 4-methyl-2,6-di-tert-butyl phenol; 2,6- di-tert-butyl phenol and 2,4-dimethyl-6-tert-butyl phenol. Good results are achieved when these antioxidants are present in the fuels of this invention in concentrations ranging from about 0.5 to about 25 pounds per 1000 barrels.

Metal deactivators can also be used to advantage in the compositions of this invention. One very suitable material is N,N-disalcylidene-1,2-diaminopropane. Generally speaking, concentrations ranging from about 0.1 to about 3 pounds per 1000 barrels are satisfactory.

Additives imparting anti-icing and anti-stalling characteristics can also be used in the fuels of this invention.

Preferred for this purpose are such materials as methanol, isopropanol, or mixtures thereof (concentrations ranging from about 0.5 to about 2 percent by volume are satisfactory); substantially neutral salts formed from primary alkyl amines and alkyl acid orthophosphates (concentrations corresponding to about 2.5 to about 25 pounds per 1000 barrels are satisfactory); and the ,B-hydroxyethyl ethylenediamine amides of oleic acid (satisfactory concentrations range from about 50 to about 200 parts per million based on the fuel). Some of these additives also confer detergency properties upon the fuels.

To overcome rumble and surface ignition, certain phosphate esters can be used. Particularly useful for this purpose are dimethyl tolyl phosphate, dimethyl xylyl phosphate, trimethylphos'phate and cresyldiphenylphosphate. Considerable care should be exercised in seeing to it that the phosphorus concentrations range from about 0.3 to about 0.6 theory of phosphorus based on the lead. A theory of phosphorus is equivalent to a phosphorusto-lead atom ratio of 2:3. If lower concentrations of phosphorus are used, the excellent exhaust valve durability characteristics of the fuels of this invention can be markedly depreciated.

Among the other additives which may be employed in the fuels of this invention are dyes, induction system cleanliness agents, top-cylinder lubricants, corrosion inhibitors, inert solvents, and alkyllead stabilizers.

We claim:

1. A self-scavenging, halogen-free, motor fuel composition for spark ignition internal combustion engines which essentially consists of a motor gasoline base stock and from about 1.20 to about 4.25 grams of lead per gallon as an alkyllead antiknock agent, the base stock being characterized by having a content of aromatic gasoline hydrocarbons ranging from about 10 to about 60 volume percent based on the Whole fuel.

2. The fuel composition of claim 1 wherein the content of aromatic gasoline hydrocarbons ranges from about 20 to about 55 percent by volume.

3. The fuel composition of claim 1 wherein said alkyllead antiknock agent is tetraethyllead.

4. The fuel composition of claim 1 wherein the 'content of aromatic gasoline hydrocarbons ranges from about 20 to about 55 percent by volume and wherein said alkyllead antiknock agent is tetraethyllead.

5. The fuel composition of claim 1 wherein said alkyllead antiknock agent is tetramethyllead.

6. The fuel composition of claim 1 wherein the content of aromatic gasoline hydrocarbons ranges from about 20 to about 55 percent by volume and wherein said alkyllead antiknock agent is tetramethyllead.

References Cited in the file of this patent UNITED STATES PATENTS 2,360,585 Ross et al Oct. 17, 1944 2,398,281 Bartholomew Apr. 9, 1946 2,593,561 Herbst et al Apr. 22, 1952 2,626,893 Morrow Jan. 27, 1953 2,852,356 Lichtenfels Sept. 16, 1958 OTHER REFERENCES Paper presented before 22d Meeting of the American Petroleum Institute, November 7, 1941, Improved Fuels Through Selective Blending, by Wagner et al., 19 pages.

Ind. and Eng. Chem., December 1948, vol. 40, No. 12, Knocking Characteristics of Hydrocarbons, by Lovell, pages 2388-2397. 

1. A SELF-SCAVENGING, HALOGEN-FREE, MOTOR FUEL COMPOSITION FOR SPARK IGNITION INTERNAL COMBUSTION ENGINES WHICH ESSENTIALLY CONSISTS OF A MOTOR GASOLINE BASE STOCK AND FROM ABOUT 1.20 TO ABOUT 4.25 GRAMS OF LEAD PER GALLON AS AN ALKYLLEAD ANTIKNOCK AGENT, THE BASE STOCK BEING CHARACTERIZED BY HAVING A CONTENT OF AROMATIC GASOLINE HYDROCARBONS RANGING FROM ABOUT 10 TO ABOUT 60 VOLUME PERCENT BASED ON THE WHOLE FUEL. 